fix: don't report game as Lobby phase when players leave mid-game

After a player left, the server would fall back to Lobby phase if player
count dropped below the max — even if the game had already started.
Now checks hasStarted() before reporting Lobby phase.

src/server/GameServer.ts

@@ -817,7 +817,7 @@ export class GameServer {
       this.gameConfig.gameType === GameType.Public &&
       this.gameConfig.maxPlayers &&
       this.activeClients.length < this.gameConfig.maxPlayers;
-    if (lessThanLifetime && notEnoughPlayers) {
+    if (lessThanLifetime && notEnoughPlayers && !this.hasStarted()) {
       return GamePhase.Lobby;
     }
     const warmupOver = now > this.startsAt! + 30 * 1000;